Summary: Cellular/Molecular
Molecular Microdomains in a Sensory Terminal, the
Vestibular Calyx Ending
Anna Lysakowski,1 Sophie Gaboyard-Niay,2* Irina Calin-Jageman,3* Shilpa Chatlani,4 Steven D. Price,1
and Ruth Anne Eatock5,6
1Department of Anatomy and Cell Biology, University of Illinois at Chicago, Chicago, Illinois 60612, 2INSERM U1051, Ho^pital Saint Eloi-Ba^timent INM,
34295, Montpellier, France, 3Department of Biological Sciences, Dominican University, River Forest, Illinois 60305, 4Committee on Neurobiology,
University of Chicago, Chicago, Illinois 60637, 5Department of Otology and Laryngology, Harvard Medical School, Boston, Massachusetts 02115, and
6Eaton-Peabody Laboratories, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts 02114
Many primary vestibular afferents form large cup-shaped postsynaptic terminals (calyces) that envelope the basolateral surfaces of type
I hair cells. The calyceal terminals both respond to glutamate released from ribbon synapses in the type I cells and initiate spikes that
propagatetotheafferent'scentralterminalsinthebrainstem.Thecombinationofsynapticandspikeinitiationfunctionsintheseunique
sensoryendingsdistinguishesthemfromtheaxonalnodesofcentralneuronsandperipheralnerves,suchasthesciaticnerve,whichhave
providedmostofourinformationaboutnodalspecializations.Weshowthatratvestibularcalycesexpressanunusualmixofvoltage-gatedNa
and K channels and scaffolding, cell adhesion, and extracellular matrix proteins, which may hold the ion channels in place. Protein
expression patterns form several microdomains within the calyx membrane: a synaptic domain facing the hair cell, the heminode
abutting the first myelinated internode, and one or two intermediate domains. Differences in the expression and localization of proteins
between afferent types and zones may contribute to known variations in afferent physiology.
Introduction
In vestibular sensory epithelia of mammals and other amniotes,